This patent application is related to the following patent applications filed herewith:
(1) U.S. patent application Ser. No. 09/561,566, entitled xe2x80x9cImplantable Medical Pump with Multi-layer Back-up Memory,xe2x80x9d filed on Apr. 28, 2000, and having named inventors David C. Ullestad and Irfan Z. Ali;
(2) U.S. patent application Ser. No. 09/562,221, entitled xe2x80x9cBattery Recharge Management for an Implantable Medical Device,xe2x80x9d filed on Apr. 28, 2000, and having named inventors Nathan A. Torgerson and James E. Riekels; and
(3) U.S. patent application Ser. No. 09/561,479, entitled xe2x80x9cMethod and Apparatus for Programming an Implantable Medical Device,xe2x80x9d filed on Nov. 1, 2001.
This invention relates generally to implantable medical devices, and more particularly to power management techniques for implantable medical devices.
The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon the medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Physicians use medical devices alone or in combination with drug therapies to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life.
Implantable medical devices are commonly used today to treat patients suffering from various ailments. Implantable medical devices can be used to treat any number of conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson""s disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. As the number of implantable medical device therapies has expanded, greater demands have been placed on the implantable medical device.
One type of implantable medical device is an Implantable Neuro Stimulator (INS). The INS delivers mild electrical impulses to neural tissue using an electrical lead. The neurostimulation targets desired neural tissue to treat the ailment of concern. For example, in the case of pain, electrical impulses (which are felt as tingling) may be directed to cover the specific sites where the patient is feeling pain. Neurostimulation can give patients effective pain relief and can reduce or eliminate the need for repeat surgeries and the need for pain medications.
Implantable medical devices such as neurostimulation systems may be partially implantable where a power source is worn outside the patient""s body. This system requires an antenna to be placed on the patient""s skin over the site of the receiver to provide energy and control to the implanted device. Typically, the medical device is totally implantable where the power source is part of the implanted device. The physician and patient may control the implanted system using an external programmer. Such totally implantable systems include, for example, the Itre(copyright) 3 brand neurostimulator sold by Medtronic, Inc. of Minneapolis, Minn.
In the case of an INS, for example, the system generally includes an implantable neurostimulator (INS) (also known as an implantable pulse generator (IPG)), external programmer(s), and electrical lead(s). The INS is typically implanted near the abdomen of the patient. The lead is a small medical wire with special insulation. It is implanted next to the spinal cord through a needle and contains a set of electrodes (small electrical contacts) through which electrical stimulation is delivered to the spinal cord. The lead is coupled to the INS via an implanted extension cable. The INS can be powered by an internal source such as a battery or by an external source such as a radio frequency transmitter. The INS contains electronics to send precise, electrical pulses to the spinal cord, brain, or neural tissue to provide the desired treatment therapy. The external programmer is a hand-held device that allows the physician or patient to optimize the stimulation therapy delivered by the INS. The external programmer communicates with the INS using radio waves.
Totally implantable medical devices, however, rely entirely on the implanted power source. Various INS components rely on the power source for energy, including for example, the signal generator for providing treatment therapy to the patient, the real time clock, the telemetry unit, and the memory. The signal generator is generally the primary energy drain for the power source. For those devices that have nonrechargeable batteries, the batteries last longer, however, the device must be surgically replaced when the power source is fully depleted. For those devices having rechargeable batteries, a surgical procedure is not required, however, the power source must be recharged more frequently since it cannot store as much energy.
In known systems, however, the continued operation of the signal generator during times of low energy unnecessarily drains the power source, thereby potentially depleting energy to device-critical INS components, such as the real time clock, the telemetry unit, and the memory. In the event that the power source runs low on energy, the implanted device can lose its treatment efficacy as well as its memory, its time, and its communications link with the external component. Further, when the power source is subsequently recharged, the INS may have to be reprogrammed and recalibrated according to the previous settings that were lost when the power source was fully depleted. The need for energy to handle the various functions of the implanted device is only going to increase.
Another disadvantage with known systems is that the power source can be damaged when it is being depleted at a high rate during periods when it has low voltage. This can occur, for example, when the implantable device is operating to provide treatment therapy with INS components having high-power requirements. For example, a 4.0 V battery that is below 2.75 V in stored energy is at risk of being damaged when it is being drained of 4 milliamps of current by the implanted device. Over time, with repeated draining of the battery at these critical setpoints would substantially reduce the efficacy of the battery and ultimately require surgical replacement of the implanted device.
Known implantable medical devices, for example, attempt to address the foregoing problems by providing low power or end-of-life warnings to the patient. For example, U.S. Pat. No. 5,344,431 discloses a method and apparatus for determination of battery end-of-service for implantable medical devices. This reference is incorporated herein by reference in its entirety. Such systems, however, continue to drain the battery until it is fully depleted without regard to preserving operation of the device-critical components.
Accordingly, there remains a need in that art to provide a power management system and technique for an implantable medical device that maintains operation of device-critical components during periods of low energy. Further, there remains a need in that art to provide a power management system and technique that allocates power source energy during periods of low energy.
The present invention provides a technique to manage and allocate the energy provided to various components of an implanted device during periods of low energy. In accordance with a preferred embodiment of the present invention, the power management system includes an implantable power source delivering energy to various components within the implantable medical device, a measurement device to measure the energy of the power source, and a processor responsive to the measurement device. The processor monitors the energy level of the power source. If the energy level falls below a first level, the processor shuts off energy to the therapy module of the implantable medical device while continuing to provide energy to the other device-critical components. If the energy level of the power source then falls below a second level, energy to even the device-critical components must be shut off. Eventually, the processor must prepare the entire implantable medical device to shut down. During recharge, when the energy level of the power source reaches a certain level, energy to all components is resumed.
Advantageously, this power management system and technique minimizes the risk of damage to the power source resulting from high energy drain during periods of low energy. Further, the present invention provides a technique to preserve operation of device-critical components of the implanted device during periods of low energy.
In alternative embodiments, the power management system of the present invention can be used with any number of implantable systems requiring a self-contained power source, including, but not limited to, pacemakers, defibrillators, and cochlear implants. In another alternative embodiment, the power management system of the present invention may be used with implantable diagnostic devices for detecting bodily conditions of certain organs, like the brain or the heart. In yet another alternative embodiment, the power management system of the present invention can be used within a drug delivery system having an implantable battery-powered pump. The power source in any of the these embodiments may be rechargeable or non-rechargeable. If rechargeable, the power source may be a lithium ion battery. The power source may also be a capacitive power source or any other source. The present invention serves to manage the energy of any of these power sources and to efficiently allocate the energy during times of low energy.